Restricting values in group of elements via XML Schema - regex

Question

I have a restriction to set on values of the element. As per the rules I want to set, following set of values are possible for my element.
<tags>
<tag>One of Audio, Video, Others.</tag>
<tag>For Audio, either Label or Record, For Video, either Studio or Producer, For Others this tag will be empty.</tag>
<tag>One of English, Spanish, French</tag>
</tags>
Now I could have set a regex pattern restriction in my XSD for a single tags element if it was plain text delimiter (,) separated values which might be
<element name="tags">
<simpleType>
<restriction base="string">
<pattern value="(Audio, (Label|Record)|Video, (Studio|Producer)|Others), (English|Spanish|French)" />
</restriction>
</simpleType>
</element>
But since I have a sequence of elements with same name tag, I am not sure it is even possible to restrict such way via XSD. I know I can restrict the values via enumeration but then I cannot group those. I want following XML to validate
<tags>
<tag>Audio</tag>
<tag>Record</tag>
<tag>English</tag>
</tags>
And following to fail validation
<tags>
<tag>Others</tag>
<tag>Record</tag>
<tag>English</tag>
</tags>
My real case is much more complex with nested restrictions, but I someone can help out in above condition, I think I can take it as a reference and solve my problem.

Answer 1

I don't think you can. If you have control of the schema why do you desire this specific rule set for validation? If you need this strict validation in this exact way you may need it done at the application level and not the document definition level. It appears what you really want is a way to tag different information based on certain tag "types". There really is no reason to have a list of elements all named tag, you know they are tags already from the parent elements name. Instead if you want validation based on the type of tags you should use different element types and structure your schema to validate against which types are allowed when and where. For your data this can be done using complex types and a choice model:
<xs:element name="audio">
<xs:complexType>
<xs:choice>
<xs:element name="Label" type="xs:string"/>
<xs:element name="Record" type="xs:string"/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:complexType name="generic">
<xs:choice>
<xs:element name="Studio" type="xs:string"/>
<xs:element name="Producer" type="xs:string"/>
</xs:choice>
</xs:complexType>
<xs:element name="video" type="generic"/>
<xs:element name="other" type="generic"/>
<xs:element name="tags">
<xs:complexType>
<xs:sequence>
<xs:choice>
<xs:element ref="audio"/>
<xs:element ref="video"/>
<xs:element ref="other"/>
</xs:choice>
<xs:element name="language">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="English"/>
<xs:enumeration value="Spanish"/>
<xs:enumeration value="French"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
I took liberty for Producer, Label, Studio, and Record that you would want the values for those types as well. If not, for your original case you can just use an attribute on the parent elements instead like this:
<xs:complexType name="generic">
<xs:attribute name="meta-type">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Studio"/>
<xs:enumeration value="Producer"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
Instead of using a choice group you could use substitutionGroups but this would require each element to be derived from the same type which you may not want.
These schema's can be expanded quite easily and if you still need a generic <tag>'s list that doesn't need strict validation you could add it as part of the tags sequence definition.
Maybe someone can give you a better answer for your original requirements, but I hope this information helps.